Ultrasonic generator and atomizer apparatus and method

ABSTRACT

A flexural resonator having predetermined resonant modes is mounted by means of a dynamic clamp which prevents movement of the resonator at the line of clamping. An electrically energized driver urges a member against the resonator exciting the predetermined resonant modes therein. The resonator may be utilized to transmit ultrasonic signals operating, for example, as a predator repellant, or as an atomizer of fluids introduced thereupon. Atomization occurs due to driver displacement amplification in the resonator at the point where fluid is directed onto the resonator surface, whereupon the fluid is thrown off of the resonator surface in small droplet form. Atomized droplet size is a function of the resonator amplitude and frequency.

Martner ULTRASONIC GENERATOR AND ATOMIZER APPARATUS AND METHOD [451 Apr.16, 1974 Primary Examiner-Lloyd L. King Attorney, Agent, or Firm-Flehr.Hohbach. Test, Albritton & Herbert [76] Inventor: John G. Martner,Atherton, Calif.

{22] Filed: July 27, 1973 57 ABSTRACT [21] Appl. No: 383,331 A flexuralresonator having predetermined resonant modes is mounted by means of adynamic clamp which prevents movement of the resonator at the line [52]239/4 239/102 ag of clamping. An electrically energized driver urges a511 lint. c .fg ml; .5168 3 8 7 8 2 member against the resonatorexciting the predeteb [58] new 0 can mined resonant modes therein. Theresonator may be utilized to transmit ultrasonic signals operating, forexample, as a predator repellant, or as an atomizer of [56] ReferencesC'ted fluids introduced thereupon. Atomization occurs due UNITED STATESPATENTS to driver displacement amplification in the resonator 3,255,8046/1966 Lang 239/102 at the point where fluid is directed onto theresonator 3,729,l38 4/1973 Tysk 239/102 surface, whereupon the fluid isthrown off of th r 3 9 7/ 1968 Engslrom ct aim 239/102 nator surface insmall droplet form. Atomized droplet g; z 3 size is a function of theresonator amplitude and freoec 3.067.948 12/1962 Lang -et al 239/4quency 25 Claims, 13 Drawing Figures H i t\\\\\\\\\\\\\ 1 l 4; P i:

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ULTRASONIC GENERATOR AND ATOMIZER APPARATUS AND METHOD BACKGROUND OF THEINVENTION est both theoretically and practically for some time.

Due to a general lack of investigative apparatus and analyticaltechniques, development has been severely limited in the area ofdesigning vibrating systems in frequency ranges higher than those rangescovered by classical equations. In the higher frequency ranges theclassical equations provided operating characteristics that departedfrom predicted design parameters. Therefore attempts to design vibratingsystemsof the type described herein were relegated entirely to empiricalmethods.

It was therefore apparent that a new approach, both experimental andtheoretical, was necessary. Some preliminary theory was described in anarticle Design of High Amplitude Resonators," in Volume 44, J. G.Martner. Journal of the Accoustical Society of America. No. 3, 7l7- 723,Sept., l968. New knowledge was applied to the design of triangular thinwedges as described in an article High Frequency Flexural Modes ofStraight Wedges, in Volume Su-l8, J. G. Martner, IEEE Transactions onSonics and Ultrasonics, No. 2, 96-103, Apr., 1971. From the baseprovided by these two works and others it was obvious that means wereneeded for providing predictable operating characteristics in practicalultrasonic generators for atomizing fluids and projecting ultrasonicenergy.

SUMMARY AND OBJECTS OF THE INVENTION There is provided an ultrasonicgenerator for atomizing fluids and for projecting ultrasonic energywhich includes a transducer for driving a dynamically clamped resonator.Dynamic clamping is attained without undue clamp mass by generatingforces at the clamp which are l80 out of phase with respect to theresonator driving forces. The driving force is spaced from the resonatorclamp and the driving frequency excites predetermined vibratory modes inthe resonator. This provides resonator displacement amplitudeamplification as compared with the driver displacement amplitude. Aresultant ultrasonic wave projection is produced and a fluid may bedirected to impinge upon the resonator surface for atomization wherebydroplets are provided having a size determined by the frequency andresonator displacement amplitude.

In general it is an object of the present invention to provide anultrasonic generator for projecting an ultrasonic energy wave having apredetermined frequency.

Another object of the present invention is to provide an ultrasonicgenerator for atmoizing a fluid impinging on the resonator atpredetermined rates of flow and for providing a predetermined medianatomized droplet size.

Another object of the present invention is to provide an ultrasonicgenerator for underwater communications.

Another object of the present invention is to provide an ultrasonicgenerator for atomizing fuel for use in internal combustion engines.

Another object of the present invention is to provide an ultrasonicgenerator for emulsifying fluids mixtures.

Another object of the present invention is to provide an ultrasonicgenerator with controlled predominating vibratory modes.

Additional objects and features of the present invention will appearfrom the following description in which the preferred embodiments areset forth in detail in conjunction with the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a sectional view of a disctype of ultrasonic generator showing the primary components.

FIG. 2 is an isometric sectional view of a stepped horn disc typeresonator showing fluid flow passages.

FIG. 3 is an isometric sectional view showing an ultrasonic generator ofthe disc type with fluid conveying passages.

FIG. 4 is an isometric sectional view of an ultrasonic generator of thedisc type having peripheral dynamic clamping.

FIG. 5 is an isometric sectional view showing an ultrasonic generator ofthe cantilevered flat plate type.

FIG. 6 is an isometric sectional view showing an ultrasonic generator ofthe tubular type.

FIG. 7 is an isometric sectional view showing an additionalconfiguration of the tubular type generator.

FIG. 8 is an isometric sectional view of a disc type ultrasonicgenerator having an isolated driving means.

FIG. 9 is an isometric sectional view of a driver showing frequency modecontrol electrodes applied.

FIG. 10 is a combination isometric sectional view and schematic diagramshowing a circuit for enhancing a specified vibratory mode.

FIG. 11 is an isometric sectional view of a driver showing frequencydoubling with auxiliary electrodes applied.

FIG. 12 is an isometric sectional view of a stacked resonator.

FIG. 13 is a detail view showing the driving and clamping points for thestacked resonator of FIG. 12.

DESCRIPTION OF THE PREFERRED EMBODIMENTS The resonators may take theform of circular or rectangular plates having a free edge or they may bein the shape of tubes having a free end. The cross section of the platesor tube walls are fabricated in varying shapes which determine theresonant frequency, the degree of amplitude amplification, and the modeof vibration in passes through the centrally located counter bore 13 andhas an integral head or flange 16 at one end which contacts the raisedportion 12 on plate 11. The other end of center post 14 threadiblyengages a base plate 17. A cylindrical electromechanical transducer 21includes half portions 22 and 23 which are bonded together on a commonplane 24. A protective drive member 26 is bonded to the top side oftransducer half portion 22. The driver member 26 is triangular in crosssection, and contacts the underside of resonator 11 along a line 27spaced from the line of contact between the raised portion 12 and flange16. A pair of electrical leads 28 are provided, one of which isconnected to the bond on common plane 24 and the other of which isconnected to the electrically common side of transducer half portions 22and 23.

The center post 14 and base plate 17 form a dynamic clamp showngenerally at 29. The manner in which dynamic clamping is obtained is asfollows. Transducer 21 is assembled by bonding transducer half portions22 and 23 together at plane 24, bonding protective drive member 26 tothe top surface of transducer half portion 22, and connecting electricalleads 28 as shown in FIG. 1. The assembled transducer 21 is placed onthe top surface of base plate 17 and the resonator disc 11 is platedatop protective drive member 26. Center post 14 is lowered through thecounter bore 13 in disc 11 for threaded engagement with base plate 17.Flange 16 is turned until transducer 21 is placed in compressionresulting in center post 14 being placed in tension. An alternatingvoltage-impressed across leads 2 8 alternately expands and contractstransducer half portions 22 and 23 within the elastic deformation rangeof the transducer material. The driving forces generated by theexpansion and contraction are directed through protective drive member26 to the resonator 11 along line 27. When the upper face of transducerhalf portion 22 expands upwardly the lower face of transducer halfportion 23 expands downwardly a like distance. Thus, any tendency forthe force applied at line 27 to push the raised portion 12 upwardly iscounteracted by a force exerted downwardly through center post 14. Theline of contact between raised portion 12 and flange 16 is preventedfrom moving in this manner.

A flange 31 projects into the bottom of the counter bore 13 in resonator11 and has an inside diameter closely fitting the diameter of centerpost 14. Flange 31 acts to maintain resonator disc 11 in a centeredposition relative to center post 14. The raised portion 12 provides apivot line for resonator disc 11 which cannot move.

FIG. 2 shows a resonator disc 11 having a stepped cross sectionalconfiguration. A thickened center portion 32 has a centrally locatedcounter bore 33 similar to the counter bore 13 in FIG. 1. A raisedportion 34 surrounds counter bore 33 on the upper surface of thethickened portion 32. A small flange 36 which may be triangular in crosssection serves to center resonator disc 11 much as the flange 31 in theconfiguration of FIG. 1. The flange 36 is also adapted to support a seal(not shown) about a center post (not shown). A chamber defined by theseal and the walls of counter bore 33 form a chamber. Passages 37 extendradially through thickened portion 32 and provide communication betweenthe chamber and an upper surface 38 of the disc 11.

The resonators 11 in FIGS. 1 and 2 may be used to project ultrasonicenergy through any medium in which they are disposed. Alternatively,when they contain passages 37 as in FIG. 2, fluid may be introduced intothe central chamber formed by the wall of the counter bore 33 and theflange 36. Fluid so introduced flows through passages 37 to bedischarged upon the surface 33. When resonator disc 11 is excited in itsresonant vibratory mode. fluid on the surface 38 is thrown offorthogonally from the surface in a mist of fine droplets.

FIG. 3 shows another embodiment similar to that of FIG. 1 but having aresonator disc 11 with a traingular or wedge shaped cross section. Theembodiment of FIG. 3 has a transducer 21. a base plate 17, andelectrical leads 28 much as the embodiment of FIG. 1. FIG. 3 also showsa raised portion 39 serving the same purpose as the raised portion 12 inFIG. 1. Raised portion 39 need not be as pronounced as raised portion 12due to the fact that the cross sectional configuration of resonator disc11 slopes downwardly from the edge of centrally located counter bore 13toward the edge of disc 11. Centering flange 31 is also present at thebottom of counter bore 13 and a center post 41 has a center bore 42extending axially into a head or flange 43. Center post 41 is configuredto threadably engage disc plate 17. A plurality of passages 44 areprovided in communication with center bore 42 passing radially throughthe flange 43.

A fluid to be atomized is directed upwardly through center bore 42 topass radially through passages 44 from which it is discharged onto theupper surface of resonator disc 11. As described above. when analternating voltage is impressed across electrical leads 28 resonatordisc 11 is excited in its resonant vibratory mode whereupon itimmediately atomizes the fluid into a cloud of microscopic dropletswhich are thrown off perpendicularly from the upper surface of disc 11.

Another embodiment of the ultrasonic generator for atomizing fluids andfor projecting ultrasonic energy is shown in FIG. 4. A resonating disc46 has a centrally located through hole 47. Around the periphery of thedisc 46 on the upper surface is a slightly raised portion 48 serving thesame purpose as the raised portion 12 in FIG. 1. It should be noted thatthe raised portion 48 need only be slight. if it exists at all, becauseof the downward slope of the upper surface of resonator disc 46. Anannular framework 49 has an upper internal flange 51 which contacts theraised portion 48 on resonator disc 46. The bottom of resonator disc 46is contacted by the transducer assembly 21 as described above which issupported by a base plate 52. The base plate 52 is fastened to thebottom of the annular framework 49 by suitable means such as screws 53.Electrical leads 28 are connected to the transducer assembly 21 asdescribed before.

When an alternating voltage is applied to the transducer through leads28 in FIG. 4, transducer assembly 21 drives resonator disc 46 into itsresonant mode of vibration. The raised portion 48 on disc 46 is clampedtightly against the underside of internal flange 51. As in theembodiments described above, annular framework 49, internal flange 51,and base plate 52 are configured to place the transducer assembly 21 incompression and to maintain that compression throughout the resonatingmodes of the disc 46. Ultrasonic vibrations may be transmitted fromresonator disc 46 through the medium in which the ultrasonic generatorof FIG. 4 is situated, or fluid may be discharged upon the surface ofresonator disc 46 for atomization as described above. It should be notedthat centrally located hole 47 is present only when design so dictates.The

modes are obtainable thereby.

Still another embodiment of the ultrasonic generator is shown in FIG. 5.A resonator 53 has a stepped configuration with a broad flat resonatingsurface 54 near the free end. and a thicker section 56 near the clampedend. Thicker section 56 has a shaped groove 57 near the clamped endcreating a thin section 58 along the length of thicker section 56. Aplurality of passages 59 extends from the V shaped groove 57 through thethicker section 56 toward the broad surface 54 near the free end of theresonator 53. A sealing strip 61 overlies the V" shaped groove 57 nearthe clamped end of the resonator 53. A backup plate 62 overlies thesealing strip 61. An "L" shaped base member 63 is provided forsupporting resonator 53. The backup plate 62 is secured to the basemember 63 by suitable means such as screws 64. A transducer 66 of amaterial which undergoes an elastic deformation in the presence of anelectric field is mounted on an insulating strip 67 which is supportedby base member 63. A protective drive member 68 is positioned atoptransducer 66, having a triangular cross section as described before,with the apex of the triangle contacting the bottom of resonator plate53 along a line horizontally spaced from the thin section 58. A pair ofelectrical leads .69 are connected to the opposite ends of transducer66.

The operation of the ultrasonic generator in FIG. 5 involves theapplication of an electrical potential across leads 64 for driving theresonator 53. Fluid is introduced into the V groove 57 eitherthrough-the ends of groove 57 or through an inlet pipe (not shown), andsubsequently passes outwardly through passages 59 to be discharged uponthe broad surface 54 near the free end of resonator 53. The fluidimpinging upon the vibrating surface 54 will be atomized as describedabove. Alternatively. the ultrasonic generator may be used to projectultrasonic energy throtigh the medium in which it is situated. It shouldbe noted that in the embodiment of FIG. 5, as in those embodimentspreviously described. the base member 63 together with that of plate 62and screws 64 is configured to place a compressive force acrosstransducer 66. Insulating strip 67 is present in this configurationbecause only a single section oftransducer 66 is used instead of the twohalf portions 22 and 23 of FIG. I. Insulating strip 67 preventselectrical potential between leads 69 from being short circuited by themetal dynamic clamp parts, base member 63, backup plate 62, and screws64.

FIG. 6 shows an embodiment of the present invention in a tubular form. Apair of upper and lower tubular sections 71 having walls with atriangular or wedge shaped cross section are formed with a free end atthe apex of the triangle or wedge and a base 72 at the opposite end. Athin section 73 connects the base 72 with an annular flange 75. Atransducer assembly 74 has two annular sections 76 and 77 which arebonded together at one end surface. Transducer protective members 78 arebonded to the remaining exposed ends of transducer section 76 and 77.Transducer protective members 78 are triangular in cross section andcontact base 72 of the tubular resonators 71 along a line 79 around thebase. Collars 81 are formed to fit around the outside of the tubularresonators 71 to rest on flanges 75. A groove 82 is cut in the collar 81leaving a flange 83 on one end of the inside diameter of collars 81.Chambers 84 are formed between the flange 83, the wall of the groove 82,flange 75, and the outside diameter of tubular resonators 71. Aplurality of passages 86 are in communication with the chambers 84extending with the free end of resonators 71, and emerging through theinner wall thereof. Collars 81 have an inlet pipe 87 extending radiallyfrom the outside diameter of the collars 81 in communication with thechambers 84. Flanges are held together by means of screws 88 whichthreadably engage flanges 75. Collars 81 are secured to flanges 75 bymeans of screws 89 which also threadably engage flange 75.

The ultrasonic generator of FIG. 6 is excited by an alternating voltageas described above. A stream of air may be passed through the center ofthe resonator tube 71 for entraining fluids atomized through impingementthereupon. Fluid may be introduced upon the resonating surface ofresonating tube 71 by directing it from a fluid source through inletpipes 87, chambers 84, and the plurality of passages 86 to be dischargednear the free end of the resonators 71. Identical resonators areprovided mounted back to back, for purposes of mechanical impedancematching, and to provide the dynamic clamping. The component parts areconfigured to place the transducer assembly 74 in compression whenscrews 88 are assembled to fasten flanges 75 together. Thin sections 73are thereby held against linear displacement by the opposing drivingforces which drive the upper and lower tubular resonators 71.

The ultrasonic generator of FIG. 6 may also be designed so that theannular transducer assembly 74 has a larger radius than that shown. Thetransducer 74 drives the resonator 71 by contacting base 72 near theperiphery of base 72. The flanges 75, in turn, are made with a smallerradius and located radially inward from the line of contact 79 withtransducer assembly 74. The radial locations of thin section 73 and base72 are re versed to accommodate positioning of the line of contact 79radially outward from thin section 73. Similarly, collars 81 and screws89 are thus positioned radially inward of the tubular section 71. Theorientation of tubular sections 71 and passages 86 are also reversedwithout impediment to the designed vibration modes of sections 71. Thisconfiguration has as its purpose prevention of direct contact of apassing gas or atomized liquid with electrically energized parts of thetransducer assembly 74.

FIG. 7 shows an embodiment much the same as the embodiment shown in FIG.6. FIG. 7 is present to show a different cross sectional configurationfor a tubular resonator 91. The tubular resonators 91 in FIG. 7 are of astepped cross sectional configuration. The remainder of the assembly inFIG. 7 is identical to that shown in FIG. 6 and like numbers apply tolike parts for performing like functions.

FIG. 8 shows yet another embodiment of the ultrasonic generator foratomizing fluids and projecting ultrasonic energy. A transducer 92 of amaterial which is elastically deformed in the presence of an, electricfield is utilized. Sections 93 and 94 are bonded together and theremaining free surfaces of transducer sections 93 and 94 have conicaltransducer protective drive members 96 bonded thereto. An insulatedelectrical lead 97 is connected to the central bond between transducersections 93 and 94 and a separate lead 97 is connected to the sidesmounting conical protective members 96. A cap 98 is securely fastened,for example by welding, to a disc shaped resonator 99. Resonator 99 hasa depending circular flange 101 having internal threads. A lower cap 102has an open end and external threads adjacent to the open end for matingwith the internal thread on depending flange 101. Leads 97 are broughtthrough a pressure seal 103 in the side of lower cap 102.

The embodiment of FIG. 8 is especially useful in explosive or flamableenvironments. The lower cap 102 is screwed into the depending flange 101so as to cause the transducer assembly 92 to be in compression at alltimes as described above. Electrical potentials on the surface of thetransducer assembly 92 are isolated from the flammable environment incommunication with the disc shaped resonator 99. A flammable fluid maytherefore be discharged upon the surface of the disc chaped resonator 99for atomization upon contact with the resonating surface without dangerof inadvertent ignition due to sparks from potential discharge.

Referring to FIG. 9 a view of a pair of annular transducer sections isshown. Upper and lower sections 22 and 23, as in FIG. 1, are shownbonded together at a common surface 24. Auxiliary electrodes 104 areshown deposited on the internal and external surfaces of the transducersections 22 and 23 for controlling signals generated piezoelectricallyon the external surfaces of transducer half .portions 22 and 23. Thetransducer material is orientated so that material expansion andcontraction takes place in a direction parallel to the cylindrical axisof annular sections 22 and 23. The open surface 106 on transducersection 22 and 107 on transducer section 23 are at electrical common orground potential. The bonded surfaces 24 receive the other side of thevoltage potential impressed across the transducer 21.

It is necessary in some ultrasonic generator designs which containnatural vibration modes too close together in frequency. to suppress oneor more of the undesirable modes. Local surface voltages having leveland phase related to vibration modes are generated on the cylindricalsides of the transducers. To suppress a mode. auxiliary electrodes 104,whose position and size are determined experimentally. are deposited onthe cylindrical sides of transducer halves 22 and 23. These auxiliaryelectrodes may be connected either to one another or to ground,depending on the signal phasing and levels generated thereon. The localsurface voltage related to an undesirable mode is either connected toground or to another similarly located electrode where a similar voltagelevel exists but of opposite phase or polarity. This connection causesradical alteration of the internal electric fields necessary to generatea given mode of vibration within the transducer body thus suppressingthe undesirable mode.

There also exists the possibility that a very desirable vibration modemight be very weak and in need of being enhanced. The internallygenerated fields are enhanced by injecting in phase signals atexperimentally determined locations on the surfaces of transducers 22and 23. This localized field enhancement causes a weak mode to becomestrong and particularly useful. The in phase signals are obtained fromthe electronic amplifier or oscillator whichever is being used to drivethe resonator itself. The in phase signals are connected to theauxiliary electrodes.

Referring to FIG. 10, a view of a similar pair of annular transducersections 22 and 23 is shown where an auxiliary electrode 104 is used aspart of a feedback loop 108 containing an amplifier and oscillator 109.In some designs it becomes difficult to match the frequency of theoscillator to the natural resonance of the transducer and resonatorsystem. Purely electronic means exist to achieve this matching. However,for the case of resonators of the type described, considerable frequencyshifting occurs due to temporary loading of the resonator surface by aliquid layer being atomized. This liquid layer effectively loads thevibrating system with extra mass and causes the system to resonate at alower frequency. It is part of the invention to provide means by whichthe oscillator and resonator systems are continually matched infrequency. This is done with the use of a feedback electrode as shown inFIG. 10. A small electrode 104 deposited on an experimentally determinedlocation on the sides of the transducer assembly containing transducerhalves 22 and 23, picks up the surface signals induced by the internallygenerated electric fields. The surface signals are connected to theinput of the oscillator at 109. This constitutes a feedback loop forcontrolling the oscillator output frequency which is amplified at 109and connected back to the common plane 24 between transducer halves 22and 23. Therafter, any change in resonator loading causes a change inresonant frequency which, by means of the feedback loop is transmittedto the oscillator at 109 which changes frequency to maintain the desireddriving frequency to maintain the design resonator frequency.

In FIG. 11 there is described yet another arrangement of auxiliaryelectrodes which provides for the creation of high frequency resonantmodes byelectrical division" of a continuous transducer crystal. It maybecome necessary to design an atomizer producing very small aerosoldroplets. as for example those which would be needed in an air purifieror humidifier application. Such apparatus requires median water dropletsof approximately 5 micron diameters entrained in an air stream. Thevibration frequencies necessary to generate this median droplet size isin excess of 500 Khz. Transducer sections for driving resonators at suchhigh frequencies are necessarily very small and thin with vibrationamplitudes so small as to be impractical and inefficient in such anapplication. To general a high frequency resonant mode with a largetransducer it becomes necessary to divide the transducer "electrically"into small vibrating portions by the addition of deposited electrodes111 on the cylindrical sides of transducer halves 22 and 23. Theelectrical connections which provide for a high frequency system usinglarge transducer halves 22 and 23 are as follows. With the upper andlower faces 106 and 107 connected to ground. the common plane interface24 must also be connected to ground. The driving output of theoscillator-amplifier apparatus 109 in FIG. 10 is connected to thecentrally located auxiliary electrodes 111 of FIG. 11. Four suchelectrodes 11 are shown and all must be connected together to thedriving output of the electrical energy source 109. This embodimentprovides a driving frequency from the transducer which is substantiallydouble that of the transducer pair 22 and 23 connected as shown in FIG.10 for example.

An embodiment is disclosed where a plurality of electrodes 111 aredeposited on the cylindrical sides of tween electrodes 111 and faces 106or 107 and between electrodes Ill and the additional electrodes. Usingthe explanation associated with the doubled frequency configurationabove it is clear that a frequency is obtained which is a multiple ofthe frequency obtained when the transducer pair is connected as in FIG.10. The multiple is the equivalent of the number of electrodes 111 onone cylindrical side of each transducer half plus one.

Polarization of the transducer halves 22 and 23 is such that the motionof the surfaces 106 and 107 are 180 out of phase. It may be seen that asingle transducer such as transducer half 22 may have electrodes llldeposited thereon. With face 106 and the face in plane 24 connected toground potential and the power supply connected to electrode 111 ontransducer 22, the transducer driving frequency is doubled as describedabove for the transducer pair, but with only one half the amplitude ofcourse.

By way of example of this arrangement, a pair of annular transducerhalves 22 and 23 one-quarter inch thick were bonded together andconnected as in FIG. 9 providing a resonant frequency of 248 Khz.Subsequently. centrally located auxilliary electrodes were deposited andconnected as shown in FIG. 11. Resonant frequency was observed as 496Khz. The resulting vibrational mode was strong and capable of driving anannular resonator l I ofthe type shown in FIG. 1 at 496 Khz. Theresulting atomizing rate experimentally obtained was I68 milliliters perminute of 6 micron median size water droplets, and the amplifier powerrequired to drive the system was 24.7 watts. This arrangement producedan ultrasonic atomizer for use in a practical air purifier.

The electrodes III of FIG. 11 may be used separately or in conjunctionwith the electrodes 104 of FIG. 9. for simultaneously suppressingunwanted vibrational modes and enhancing and maintaining those modeswhich are desirable. Either piezoelectrical or electrostrictivematerials may be used for the transducer 2! described above.

Referring to FIG. 12 a sectional view of an embodiment including stackedresonators is shown. The dynamic clamp and the driver components areidentical to those described in FIG. I and are given like numbers. Anupper resonator 112 has a central hole 113 having a raised portion 114surrounding the upper edge. A lower resonator 116 also has a centrallylocated hole 117 and a circular raised portion 118 on the upper surfaceof resonator 116 with a larger diameter than the raised portion I14. Theline of contact 27 is on a greater diameter than the raised portion I18.When the ultrasonic generator with stacked resonators is assembled araised portion 114 is in contact with the underside of the flanged head16 on the center post 14. The raised portion 118 on resonator 116 is incontact with the underside of upper resonator 112. As described above.dynamic clamping is obtained at the raised portion I14, and greateramplitudes along the length of lower resonator 116 are attainable due tothe translational displacement occurring at the raised portion 118 onlower resonator 116.

The purpose of stacked resonators is to provide a large vibrationamplitude over a large surface to gain a greater fluid volume ofatomization per unit time. To obtain the advantages promised by thisconfiguration of the invention reference is made to FIG. 13. Thecondition for balanced resonance in a stacked resonator embodiment is:

In the above relationship m, represents the mass of the upper resonator112 on one side of the fulcrum represented by raised portions 118 asindicated in FIG. 13. M l is equivalent to the mass of the upperresonator 112 on the opposite side of the fulcrum represented by raisedportion 118. m is the mass of that portion of the lower resonator 116 onone side of the line of contact 27, and M represents the mass ofresonator 116 on the opposite side of line of contact 27 as shown againin FIG. 13. The distance A is the radial distance between the raisedportion 114 and the raised portion 118. The distance A is the radialdistance between the raised portion 118 and the line of contact 27. Thedistance I, is the radial distance from the raised portion 114 to theouter edge of the upper resonator 112. The distance is the radialdistance from the line of contact 27 to the outer edge of the lowerresonator 116.

The concept of the dynamic clamp, as disclosed herein, is that devicewhich prevents a moving or vibrating'cantilevered piece from displacingthe clamping point or line in any direction. It is difficult to achieveabsolute clamping with a static clamp since the mass of the clamp mustbe considerably larger than that of the vibrating system to preventmovement of the clamping line by the inertial forces generated in thevibrating system. To circumvent the use of large masses in the clampwhile still achieving the required clamping stability, the inertialforces generated within the system supplement. or wholly substitute forthe mass of the clamp. The generated forces are transferred through theclamping structure to the desired point for applying forces opposing thedriving forces tending to move the clamping line. This is a commoncharacteristic in all of the embodiments described. The path for thetransmission of the opposing forces to the clamping line is purposelykept to a length less than one quarter wave length of the drivingfrequency in the medium from which the clamp is made. This designconsideration keeps the opposing forces and the driving forcesreasonably close to a 180 phase relationship. Referring to FIG. 1 it maybe seen that neglecting phase lag in either'the driving force or theopposing force, an equal and opposite force would arrive at the clampingline on clamping is attained and the clamping line 12 is heldsubstantially motionless. The dynamic clamping derived from compressiveforces within the transducer is necessary to the proper control of thevibratory mode in flexure in any of the resonators described herein.

Due to the complexity of the physical phenomenon involved in themechanical application of high frequency vibration modes of finitesolids, a set of equations has been developed which are capable ofsolution with the aid of digital computer equipment. Certain of thefactors contained in the equations are obtained empirically. Examples ofthese empirical factors are those related to mechanical coupling withgaseous media when the ultrasonic generator is used to projectultrasonic vibrations, and mechanical coupling with a liquid media ofvarying layer thickness when the ultrasonic generator is utilized as anatomizer. Cross sectional shape and inclusion of channels within theresonators to carry liquids to points of maximum vibration amplitudealso affect the vibratory modes of the resonators. By way ofillustration of the method used to arrive at a cross sectional shape fora resonator with predictable vibratory modes which may be driven atultrasonic frequencies (20 to 2000 Khz), the following is set forth fordisc shaped type resonators such as that shown in FIG.

The design of a resonator of the disc type must start by considering theclassical differential equations of the transverse displacements w atany point on the disc. The displacement w is given by:

In the above relationship d is the flexural rigidity of the platematerial and is determined from the following relationship:

in the relationship for flexural rigidity the symbols are identified asfollows:

E Youngs Modulus h plate thickness p. mass density per unit area p hPoisson's ratio (dispersive property of vibration velocity in plates.)

in equation (a) above:

v4 v2 .va

where V is the Laplacian operator expressed in polar coordinates asfollows:

V 5 /8 r l/r l/r 6 /59 In the last expression r is the radius and 6 isthe direction angle. Assuming free vibration. the displacement is:

w W cos w! is on one surface of the resonator just prior to beingatomized. the equation (a) becomes:

K in the latter equation is the stiffness of the medium measured inunits of force per length unit of deflection per unit area of contact.

The following relationships have as their purpose to find an equationthat relates vibration frequency to resonator dimensions and theproperties of the resonator material. When vibrating a plate or parts ofa plate, twisting and bending moments are related to the dis placement wby:

(r) Transverse shearing forces must also be considered which may berepresented by:

Qr (V Q@=D mas/250W WT- The edge reactions are: 7

(h) The strain energy of twisting and bendingis in polar form:

Llw

lib-1:2

The above system of equations is solved assuming Fourier components in 9providing the following:

W r.s)= i Wn(r) cos n9+ i W: (r) sin n0 (j) Th the latter relationship:1 is the numberofnodal diameters for a particular mode of resonance.Substituting equation (j) into equation (d) one obtains:

(k) An identical relationship exists for W These equations (k) are formsof Bessel's equation with the solution:

In the Bessel equations J". Y are first and second kind of Besselfunctions and I K, are modified Bessel functions of the first and secondkind. The terms A,. through D,, determine the mode shape and areobtained from the boundary conditions of the particular resonator type.

The general solution to equation.(c) above is:

W j [A,.J,.(Kr) Bur .410 0.1.00

+: 1.00 lemma] Sin n0 (n) The equations (a) through (m) are generalequations and are known relationships. In order to design usefulresonators one must first determine the proper boundary conditionsapplicable to the particular design, introduce these boundary conditionsinto the proper equations above, solve the equations and thus determinethe proper frequency parameters A that are used in the frequencyequations for a particular shape resonator. The equations (a) to (m)above are especially applicable to disc shaped atomizer resonators. Toapply these equations to plate or tubular type resonators it becomesconvenient to change the coordinate system from polar to eitherorthogonal, skew, or some other suitable system depending on whether theatomizer is rectangular, tubular, or some other shape.

By way of example, the design of a resonator of a disc type isundertaken which is assumed to be free to vibrate at the periphery andhaving a radius a. The boundary conditions are:

V,- (a)=O (A) These latter two relationships are valid since the bendingmoment M, and the edge reaction V, are zero. Using equations (f), (g)and (h) it can be shown that the boundary conditions for M, and V, givethe following frequency equation:

(B) The roots of this'last equation are located between the zeros of thefunction 1,, (A) and J (A) and larger roots may be calculated from theseries:

(C) where m 4n 8L 7 1r/2 (n+2s) Values of A which arethe frequencyparameters being sought. have been computed in Volume 24, Coldwell etal. Phil. Mag., ser. 7'. No. 165, page 1041 (i937), and are presented inTable form. Once the values for the parameter X are found, they are usedto determine the physical dimensions of a desired resonator and appliedto the specific equation for the resonator type. In this instance:

A wa V p.715 where f= w/21r Solving the relationship (D) for thefrequency f which is desired, design parameters for a given resonatorare obtained.

Since some of the resonators disclosed herein are annular shaped discsthe center hole radius is designated b. The following reference containsX values for this type of resonator which may be used as a firstapproximation for a specific design; Volume 14, Raju, P.N., Journal ofthe Aeronautical Society of India, No. 2, page 37 I962). Modificationsare required to account for the mode of driving, the desired localvibration amplitude distribution, the location of nodal lines, and theinclusion of liquid flow passages and support points.

By way of further application of the above equations the following isset forth. Assume the design of an atomizer is desired which iscentrally clamped and which must vibrateat a resonant frequency of 62kilohertzf The selection of this frequency is for the purpose ofproducing an atomized fluid with droplet sizes centering on 15 microns.First a determination of the frequency parameter A for the shape desiredis undertaken. The shape here will be that of a circular disc of uniformcross section that must contain a hole in the center to provide for theproper driving system which will be similar to that shown in FIG. I. Thefrequency parameter A is determined from proper solutions to I)equationsta) through (m) which are modified by the suitable boundaryconditions. A computer program has been devised that allowsdetermination of eigen solutions for different nodal configurations. Theradius of the centrally located hole is represented by the'symbol b andthat of the outer rim by the symbol a". The disc thickness isrepresented by h and the number of nodal diameteis by n". The number ofnodal circles is represented by .r". The following frequency parametersare obtained for various combinations of n and s.

A logical design dimension ratio of b/a 0.3 was chosen. It can be shownthat the corresponding frequency parameters A for given values of n ands are:

Assuming a central hole radius to be 0.79 centimeter, the outer rimradius becomes 2.64 centimeters. The equation for an annular typeresonator free at the rim and clamped at the inner rim is:

Where: a is Poissons ratio and 0 0.33 for aluminum.

45.27 Khz f2: 61.60 Khz f 81.23 Khz,

From the above it is seen that the value of f approaches the designfrequency of 62 Khz. This provides a disc which will vibrate with twonodal diameters and one nodal circle, is fabricated from aluminum, andhas the above dimensions. This resonator is clamped in the mannerdescribed in FIG. 1 showing the transducer bonded to the base platemember 17 which provides the dynamic clamp that is part of thisinvention.

A typical driving system for the invention disclosed herein of the typeshown in FIG. 1 might have the following dimensions by way of example.The transducer assembly 21 may be l inch long by 1 inch in diameter. Thecenter post 14 may be 0.3 inches in diameter and the flange 16 may be0.8 inches in diameter. The center post 14 may be 2 inches long. Whenthe system is assembled it is tightened across the transducer 21 justsufficiently to provide a compressed assembly so that upon vibrating thetransducer is never allowed to reach an uncompressed state where itwould chatter against the underside of the resonator 11.

As may be seen by the above design analysis for an annular discresonator the mode f is 45.27 Khz and provides the largest vibrationamplitude. To effectively suppress this mode it becomes necessary topaint a set of shorting electrodes on the surface of the transducer. Thelocation and the size of the electrodes are determined experimentallyfrom a rigorous surface motion plot which is done with a suitablevibration pickup apparatus.

In the above example an atomizer was produced with an actual resonantfrequency of 59.1 Khz with a rate of atomization of H35 cubiccentimeters of water per minute. The power consumption of the transducerwas l8.2 watts and a feedback loop such that at 108 containing a twotransistor amplifier such as that at 109 in FIG. 10 was used forcontrolling the desired driving frequency.

An ultrasonic generator for use in atomizing fluids and for projectingultrasonic energy through a medium has been devised having a low massdynamic clamp, allowing resonant mode control, and providing a methodfor designing resonators with predictable operating characteristics.

1 claim:

1. An ultrasonic generator ofthe type energized from an electricalenergy source comprising a resonator. transducer means connected to saidelectrical energy source and responsive to electrical energy to expandand contract, said transducer means including means for engaging saidresonator along a line of contact spaced from one edge of the resonator,and clamping means for engaging said one edge and said transducer meansto clamp said transducer means between said resonator and said clampwhereby a predetermined vibration mode is induced in said resonator whensaid transducer means is energized producing a displacement amplitude insaid resonator which is an amplification of the displacement amplitudeof said transducer means.

2. An ultrasonic generator as in claim 1 wherein said resonatorcomprises a disc having a free peripheral area, and wherein saidclamping means centrally engages said disc.

3. An ultrasonic generator as in claim 1 wherein said resonatorcomprises an upper resonator, a lower reso nator, said upper resonatorbeing contacted by said clamping means, said lower resonator beingcontacted by said means for engaging said resonator along the line ofcontact. and additional means for providing a line of contact betweensaid upper and lower resonators, said additional means located betweensaid upper resonator contact and said lower resonator contact lineswhereby a larger surface of high vibration amplitude is provided on saidlower resonator surface for increasing the rate of atomization of fluidsimpinging thereupon.

4. An ultrasonic generator as in claim 2 wherein said disc is annularhaving a plurality of fluid passages leading from the center thereoftowards said displacement amplification for delivering fluids thereto.

5. An ultrasonic generator as in claim 1 wherein said resonatorcomprises a disc having a free central area, and wherein said clampingmeans peripherally contacts said disc at said one edge.

6. An ultrasonic generator as in claim 5 wherein said disc is annular inshape.

7. An ultrasonic generator as in claim 1 wherein said resonatorcomprises a tube having an inner wall, an outer wall, and a base,wherein said clamping means comprises a base flange and a relativelythin section connecting said base flange and one edge of said base, andwherein said transducer means contacts said tube along a line of contactnear the outer edge of said base.

8. An ultrasonic generator as in claim I wherein said resonatorcomprises a pair of tubes each having a free end, wherein said one edgeis a base, wherein said clamping means comprises a base flange for eachof said tubes, a relatively thin section connecting each of said flangesto said one edge, and means for fastening said base flanges securelytogether, wherein said transducer means contacts said one edge along aline on each of said pair of tubes.

9. An ultrasonic generator as in claim 8 togetherwith means adjacentsaid base for forming a channel for receiving fluids, and wherein saidtubes have a plurality of passages therethrough in communication withsaid channel and extending toward said free end.

10. An ultrasonic generator as in claim 8 wherein said relatively thinsection is connected to the central edge of said base flange, and saidtransducer means contacts the peripheral edge of said base.

11. An ultrasonic generator as in claim 8 wherein said relatively thinsection is connected to the peripheral edge of said base flange and saidtransducer means contacts the central edge of said base.

12. An ultrasonic generator as in claim 1 wherein said resonatorcomprises a plate having a free end opposite from said one edge, whereinsaid clamping means comprises a base member, and a relatively thinsection connecting said one edge with said base member, and wherein saidtransducer mea'ns contacts said plate near said one edge.

13. An ultrasonic generator as in claim 12 together with means adjacentsaid base member forming a channel for receiving fluids, and whereinsaid plate has a plurality of passages therethrough in communicationwith said channel and extending toward said free end.

14. An ultrasonic generator as in claim I wherein said clamping meansfrom said one edge to said transducer means which is less than onequarter wavelength of the driving frequency in the medium of saidclamping means.

15. An ultrasonic generator as in claim 1 wherein said transducer meanscomprises a solid having first and second opposite sides exhibitingdisplacement due to elastic deformation induced by an electric field, aprotective driving member secured to said first side of said transducerfor contacting said resonator. an insulator for insulating said secondside of said transducer from said clamping means, and electricalconnections to said first and second sides from said electrical energysource.

16. An ultrasonic generator as in claim 1 wherein said transducer meanscomprises a solid having first and second opposite sides exhibitingdisplacement due to elastic deformation induced by an electric field, aprotective driving member secured to said first side for contacting saidresonator, additional sides on said transducer means orthogonal to saidfirst and second opposite sides, and means centrally located on saidadditional sides for connecting one side of said electrical energysource, whereby when said first and second sides are connected in commonto the other side of said electrical energy source said transducerprovides a driving frequency substantially double that provided whensaid electrical energy source is connected to said first and secondopposite sides.

l7. An ultrasonic generator as in claim I-- wherein said electricalenergy source has an output terminal and a common terminal and whereinsaid transducer means comprises at least one pair of transducersexhibiting displacement due to elastic deformation induced by anelectric field. first and second opposite sides on said transducers,said first sides being secured together in electrical contact so thatsaid second sides provide displacement 180 out of phase when saidtransducer means is energized. additional sides on said transducersorthogonal to said first and second opposite sides, means centrallylocated on said additional sides for connecting said electrical energysource output terminal, whereby when said first and second sides areconnected to said common terminal said transducer provides a drivingfrequency substantially double that provided when said output and commonterminals are connected to said first and second sides respectively.

18. An ultrasonic generator as in claim 1 wherein said electrical energysource has an output terminal and a common terminal and wherein saidtransducer means comprises at least one pair of transducers exhibitingdisplacement due to elastic deformation induced by an electric field,first and second opposite sides on said transducers, said first sidesbeing secured together in electrical contact so that said second sidesprovide displacement 180 out of phase when said transducer means isenergized, additional sides on said transducers orthogonal to said firstand second opposite sides, first means located on said additional sidesfor connecting said output terminal. second means located on saidadditional sides for connecting said common terminal, said first andsecond means for connecting being alternately positioned and equallyspaced from one another and said first and second sides whereby whensaid first and second sides and said second means for connecting areconnected to said common terminal and said first means for connectingare connected'to said output terminal, said transducer provides adriving frequency substantially a multiple of that provided when saidoutput and common terminals are connected to said first and second sidesrespectively, said multiple being equivalent to the number of said firstconnecting means on one of said additional sides of one transducer ineach pair plus one.

19. An ultrasonic generator as in claim 1 wherein said transducer meanscomprises a pair of transducers exhibiting displacement due to elasticdeformation induced by an electric field, said transducers havingadjacent first sides secured together in electrical contact and oppositefacing second sides, a pair of protective driving members secured tosaid second sides, and electrical connections to said first and secondsides from said electrical energy source.

20. An ultrasonic generator as in claim 19 wherein said transducer meanshave additional sides, together with at least one electrode attached toa selected position on one of said additional sides, said selectedposition exhibiting a voltage related to said predetermined vibrationmode, a source of voltage in phase with the voltage at said selectedposition and means for connecting said source of in phase voltage tosaid one electrode for enhancing said predetermined vibration mode.

21. An ultrasonic generator as in claim 19 wherein a varying mass loadis applied to the surface of said resonator and wherein said transducermeans have additional sides, at least one additional electrode attachedto a selected position on one of said additional sides, said selectedposition exhibiting a voltage related to said predetermined vibrationmode, feedback means for receiving said voltage related to predeterminedvibration mode, said feedback means connected to said electrical energysource, whereby said transducer is driven to maintain said voltage atsaid selected position and thereby to maintain said predeterminedvibration mode.

22. An ultrasonic generator as in claim 19 wherein said transducers haveadditional sides and wherein said additional sides exhibit voltagesrelated to vibration modes in the ultrasonic generator, together with atleast one electrode overlying a selected area on one of said additionalsides. and a ground connection from said one electrode for alteringinternal transducer electrical fields and suppressing undesirablevibration modes.

23. An ultrasonic generator as in claim 19 wherein said transducers haveadditional sides and wherein said additional sides exhibit voltagesrelated to vibration modes in the ultrasonic generator, together with atleast one electrode overlying a selected area on one of said additionalsides, at least one additional electrode overlying a selected area onanother of said additional sides, an electrical connection between saidselected areas, said selected areas having similar voltage levels but ofopposite polarity, whereby internal transducer electrical fields arealtered for suppressing undesirable vibration modes.

24. The method of producing ultrasonic energy waves comprising the stepsof predetermining the resonant modes of a member, clamping the memberdynamically along a line at one end, and driving the member in flexurealong a line spaced from the clamping feet for controlling the drivingfrequency of the member to maintain the resonant mode, whereby the fluidis atomized forming a cloud having a predetermined median droplet size.

1. An ultrasonic generator of the type energized from an electricalenergy source comprising a resonator, transducer means connected to saidelectrical energy source and responsive to electrical energy to expandand contract, said transducer means including means for engaging saidresonator along a line of contact spaced from one edge of the resonator,and clamping means for engaging said one edge and said transducer meansto clamp said transducer means between said resonator and said clampwhereby a predetermined vibration mode is induced in said resonator whensaid transducer means is energized producing a displacement amplitude insaid resonator which is an amplification of the displacement amplitudeof said transducer means.
 2. An ultrasonic generator as in claim 1wherein said resonator comprises a disc having a free peripheral area,and wherein said clamping means centrally engages said disc.
 3. Anultrasonic generator as in claim 1 wherein said resonator comprises anupper resonator, a lower resonator, said upper resonator being contactedby said clamping means, said lower resonator being contacted by saidmeans for engaging said resonator along the line of contact, andadditional means for providing a line of contact between said upper andlower resonators, said additional means located between said upperresonator contact and said lower resonator contact lines whereby alarger surface of high vibration amplitude is provided on said lowerresonator surface for increasing the rate of atomization of fluidsimpinging thereupon.
 4. An ultrasonic generator as in claim 2 whereinsaid disc is annular having a plurality of fluid passages leading fromthe center thereof towards said displacement amplification fordelivering fluids thereto.
 5. An ultrasonic generator as in claim 1wherein said resonator comprises a disc having a free central area, andwherein said clamping means peripherally contacts said disc at said oneedge.
 6. An ultrasonic generator as in claim 5 wherein said disc isannular in shape.
 7. An ultrasonic generator as in claim 1 wherein saidresonator comprises a tube having an inner wall, an outer wall, and abase, wherein said clamping means comprises a base flange and arelatively thin section connecting said base flange and one edge of saidbase, and wherein said transducer means contacts said tube along a lineof contact near the outer edge of said base.
 8. An ultrasonic generatoras in claim 1 wherein said resonator comprises a pair of tubes eachhaving a free end, wherein said one edge is a base, wherein saidclamping means comprises a base flange for each of said tubes, arelatively thin section connecting each of said flanges to said oneedge, and means for fastening said base flanges securely together,wherein said transducer means contacts said one edge along a line oneach of said pair of tubes.
 9. An ultrasonic generator as in claim 8together with means adjacent said base for forming a channel forreceiving fluids, and wherein said tubes have a plurality of passagestherethrough in communication with said channel and extending towardsaid free end.
 10. An ultrasonic generator as in claim 8 wherein saidrelatively thin section is connected to the central edge of said baseflange, and said transducer means contacts the peripheral edge of saidbase.
 11. An ultrasonic generator as in claim 8 wherein said relativelythin section is connected to the peripheral edge of said base flange andsaid transducer means contacts the central edge of said base.
 12. Anultrasonic generator as in claim 1 wherein said resonator comprises aplate having a free end opposite from said one edge, wherein saidclamping means comprises a base member, and a relatively thin sectionconnecting said one edge with said base member, and wherein saidtransducer means contacts said plate near said one edge.
 13. Anultrasonic generator as in claim 12 together with means adjacent saidbase member forming a channel for receiving fluids, and wherein saidplate has a plurality of passages therethrough in communication withsaid channel and extending toward said free end.
 14. An ultrasonicgenerator as in claim 1 wherein said clamping means from said one edgeto said transducer means which is less than one quarter wavelength ofthe driving frequency in the medium of said clamping means.
 15. Anultrasonic generator as in claim 1 wherein said transducer meanscomprises a solid having first and second opposite sides exhibitingdisplacement due to elastic deformation induced by an electric field, aprotective driving member secured to said first side of said transducerfor contacting said resonator, an insulator for insulating said secondside of said transducer from said clamping means, and electricalconnections to said first and second sides from said electrical energysource.
 16. An ultrasonic generator as in claim 1 wherein saidtransducer means comprises a solid having first and second oppositesides exhibiting displacement due to elastic deformation induced by anelectric field, a protective driving member secured to said first sidefor contacting said resonator, additional sides on said transducer meansorthogonal to said first and second opposite sides, and means centrallylocated on said additional sides for connecting one side of saidelectrical energy source, whereby when said first and second sides areconnected in common to the other side of said electrical energy sourcesaid transducer provides a driving frequency substantially double thatprovided when said electrical energy source is connected to said firstand second opposite sides.
 17. An ultrasonic generator as in claim 1wherein said electrical energy source has an outpuT terminal and acommon terminal and wherein said transducer means comprises at least onepair of transducers exhibiting displacement due to elastic deformationinduced by an electric field, first and second opposite sides on saidtransducers, said first sides being secured together in electricalcontact so that said second sides provide displacement 180* out of phasewhen said transducer means is energized, additional sides on saidtransducers orthogonal to said first and second opposite sides, meanscentrally located on said additional sides for connecting saidelectrical energy source output terminal, whereby when said first andsecond sides are connected to said common terminal said transducerprovides a driving frequency substantially double that provided whensaid output and common terminals are connected to said first and secondsides respectively.
 18. An ultrasonic generator as in claim 1 whereinsaid electrical energy source has an output terminal and a commonterminal and wherein said transducer means comprises at least one pairof transducers exhibiting displacement due to elastic deformationinduced by an electric field, first and second opposite sides on saidtransducers, said first sides being secured together in electricalcontact so that said second sides provide displacement 180* out of phasewhen said transducer means is energized, additional sides on saidtransducers orthogonal to said first and second opposite sides, firstmeans located on said additional sides for connecting said outputterminal, second means located on said additional sides for connectingsaid common terminal, said first and second means for connecting beingalternately positioned and equally spaced from one another and saidfirst and second sides whereby when said first and second sides and saidsecond means for connecting are connected to said common terminal andsaid first means for connecting are connected to said output terminal,said transducer provides a driving frequency substantially a multiple ofthat provided when said output and common terminals are connected tosaid first and second sides respectively, said multiple being equivalentto the number of said first connecting means on one of said additionalsides of one transducer in each pair plus one.
 19. An ultrasonicgenerator as in claim 1 wherein said transducer means comprises a pairof transducers exhibiting displacement due to elastic deformationinduced by an electric field, said transducers having adjacent firstsides secured together in electrical contact and opposite facing secondsides, a pair of protective driving members secured to said secondsides, and electrical connections to said first and second sides fromsaid electrical energy source.
 20. An ultrasonic generator as in claim19 wherein said transducer means have additional sides, together with atleast one electrode attached to a selected position on one of saidadditional sides, said selected position exhibiting a voltage related tosaid predetermined vibration mode, a source of voltage in phase with thevoltage at said selected position and means for connecting said sourceof in phase voltage to said one electrode for enhancing saidpredetermined vibration mode.
 21. An ultrasonic generator as in claim 19wherein a varying mass load is applied to the surface of said resonatorand wherein said transducer means have additional sides, at least oneadditional electrode attached to a selected position on one of saidadditional sides, said selected position exhibiting a voltage related tosaid predetermined vibration mode, feedback means for receiving saidvoltage related to predetermined vibration mode, said feedback meansconnected to said electrical energy source, whereby said transducer isdriven to maintain said voltage at said selected position and thereby tomaintain said predetermined vibration mode.
 22. An ultrasonic generatoras in claim 19 wherein said transducers have additional sides andwherein said additional sides eXhibit voltages related to vibrationmodes in the ultrasonic generator, together with at least one electrodeoverlying a selected area on one of said additional sides, and a groundconnection from said one electrode for altering internal transducerelectrical fields and suppressing undesirable vibration modes.
 23. Anultrasonic generator as in claim 19 wherein said transducers haveadditional sides and wherein said additional sides exhibit voltagesrelated to vibration modes in the ultrasonic generator, together with atleast one electrode overlying a selected area on one of said additionalsides, at least one additional electrode overlying a selected area onanother of said additional sides, an electrical connection between saidselected areas, said selected areas having similar voltage levels but ofopposite polarity, whereby internal transducer electrical fields arealtered for suppressing undesirable vibration modes.
 24. The method ofproducing ultrasonic energy waves comprising the steps of predeterminingthe resonant modes of a member, clamping the member dynamically along aline at one end, and driving the member in flexure along a line spacedfrom the clamping line, whereby the resonant modes of the member areexcited.
 25. The method of producing ultrasonic energy as in claim 24together with the steps of introducing a fluid upon the surface of themember, sensing the loading effect of the fluid, and utilizing thesensed loading effect for controlling the driving frequency of themember to maintain the resonant mode, whereby the fluid is atomizedforming a cloud having a predetermined median droplet size.